also, it REALLY depends on what you're after. for all of my hiking and backpacking, I prefer tactical bags.
http://www.511tactical.com/All-Products/Bags-Backpacks/Backpacks/RUSH-72-Backpack.html here's a link to my current favorite, I can drop 2x 100' rolls of rope into the bag, 5 MRE's, 2 rappelling harnesses, 2 chalk bags, 2 3L camelbacks, a large collection of carabiners and descenders, a large bag of trail mix, and 2 changes of clothes. My backpack straps to the top, the bottom, or the back, wherever I want to put it. I could easily strap a small tent to it as well. In addition, I could fit up to a 17" laptop (or a ballistic plate) in the back as well...
they ride nicely on your back and are reasonably small, with no hard frame at all, easy to fly it if you need to, in fact, I use it as my carry on whenever I fly.